A new technique has been conceived for measuring pulmonary parameters in non-cooperative subjects, particularly infants and children. Known volumes of tracer gases are synchronously introduced into a nostril early enough in the inspirations to insure that all the tracer goes into the alveolar compartment. Alveolar gas is sampled during each expiration with special automated gas samples. Using helium, acetylene, dimethylether, and Freon-12 as tracers, continuous monitoring of effective pulmonary blood flow, FRC, alveolar ventilation, O2 uptake, and CO2 production, can be achieved. The method should be blind to left-to-right shunts, a hypothesis which will be tested with young children with congenital heart defects. Measurement of VA/Qc imbalance is provided by the data from three soluble gases when applied to a three compartment model, validation with dogs, having induced VA/Qc imbalance will be provided by the simultaneous application of a modification of the multiple inert gas method of Wagner and West. Validations of VA, O2 uptake, CO2 production, and FRC will be performed directly with sick neonates receiving ventilatory support. A portable unit will be built using a three channel gas chromatograph as the analyzer, to provide sufficient sensitivity for measuring the low concentrations compatible with continuous breathing of the tracer gases. A clinical study employing this new method will be applied to infants with respiratory distress syndrome (RDS) who are managed with continuous distending pressure therapy (CDP).